Trucks utilizing automated mechanical transmissions (also referred to as automated manual transmissions) depend on gear shifting logic or algorithms to determine the appropriate gear for a wide variety of conditions. Each shift decision may be based on a balance between fuel efficiency and performance to provide a desired driving experience. One of the significant parameters impacting this balance is the total mass or weight of the vehicle. For example, a truck carrying no payload may shift to a higher gear by skipping one or more gears to improve fuel efficiency and yet still maintain an adequate level of performance. However, a truck carrying a heavy payload may upshift through each gear and engage each gear for a longer period of time to improve performance by transmitting an increased amount of power from the engine.
Some systems rely on the equation for Newton's second law of motion, force=mass*acceleration, to calculate a vehicle's mass or weight for use in a shifting algorithm. For example, the engine torque is related to the force that propels the vehicle. When the engine torque is known, the vehicle mass may be derived through a calculation based on the vehicle's acceleration. A system may repeat the calculation several times to provide a more accurate mass or weight value.
The vehicle must be in motion for this mass determination method to work because it requires measurement of a useful acceleration value. Also, this method typically uses an average of several calculations, and a single inaccurate calculation may adversely impact the mass or weight value. Furthermore, collecting and averaging several calculations takes time during which shifting performance may be negatively affected.
Gear shifting logic or algorithms for automated mechanical transmissions used in tanker trucks that transport various liquids present additional challenges. For example, a tanker truck may refer to a truck with a tank affixed to the truck chassis, or a truck tractor pulling a trailer with a tank. Liquid in a tank responds to acceleration or deceleration by displacing, keeping its surface perpendicular to the combined gravity and acceleration or deceleration forces. The kinetic energy of the liquid in the tank is increased or decreased through its interaction with the tank surfaces. A tank that is filled to less than full capacity allows the liquid to move from front to back or back to front during acceleration or deceleration. This movement of liquid is referred to as sloshing. If the sloshing results in a significant and sudden transfer of kinetic energy to or from the liquid in the tank, the transfer effectively imparts a force against the front or back ends of the tank which may affect the vehicle acceleration or deceleration.
The force of the sloshing liquid imparted to the vehicle may result in inaccurate mass-estimations because the force may cause a sudden acceleration or deceleration of the vehicle. Further, if a sloshing force is imparted during a transmission gear shift, the intended gear ratio may not be engaged in a manner that ensures a comfortable, safe ride, or the intended gear may not be engageable at all, which may create an unstable and sometimes hazardous driving situation.